That's great that you finally have a keyboard, and want to develop your skills! I agree with JK that getting a GOOD teacher is imperative. Granted, you can learn on your own to some degree, but if you are really serious as you state, you certainly will want to have someone there to make sure you are not developing bad habits...(believe me, once developed, very difficult to correct), and you are bound to have questions along the way. It also depends why you have have gotten serious about playing. What do you want to do with it? Do you want to play purely for enjoyement? Do you want to teach one day, or perform? If you are thinking about doing something with piano as a career, you would probably be best starting with an instructer who can guide you properly.
You said your parents bought you the keyboard? Are they supportive of your goals. Have you discussed with them how serious you are about playing? Is it possible that they may be able to afford the lessons for you?
If not, you may consider raising the money on your own, babysitting, mowing lawns, part-time job, etc. It is important to find a "good" teacher, however you may find one that is somewhat less expensive by doing one of the following:
1. Contact a church and find out who the pianist/organist are. Many times these individuals give
lessons on the side and are not as expensive.
2. Check with the community colleges. Sometimes during the summer they will offer 6-8 week courses on beginning piano I, then II, them III, etc. Even if they do not have an actual keyboard/piano class, almost all of them have Basic Music Theory.
3. Check with your local University's and Colleges....often senior students majoring in piano performance will be looking for ways to supplement their income.
4. You might even check with local music shools/studios in your area. You may be able to work out some sort of an agreement with them to where you do clerical/reception type work a couple hours, a couple days a week in exchange for lessons! I know if a young person came to me with a desire to learn and wanting to work, I surely would come up with something.

While you are checking these leads out, you are bound to be given names of others who teach. Hopefully after speaking with your parents and letting them know you are serious, they will be able to help, but no matter what, if this is something you truly want, don't give up!
Best of Luck and let us know how you are doing!
s
